264 
SECOND REPORT - 1832 . 
Rosin ..96 
Sealing-wax.95 
Crown glass.90 
China ink ..88* 
Ice.85 
Minium.80* 
Isinglass.80 
Plumbago. ... 75 
Thick film of oil.59 
Film of jelly.54f 
Thinner film of oil .........51f 
Tarnished lead..45 
Film of jelly, (£ of former quantity) 38 
Tin scratched with sand-paper ... 22 
Mercury .. . 20 
Clean lead.19 
Polished iron ....15 
Polished tin, gold, silver, copper . . 12 
Thin lamina of gold, silver, or cop¬ 
per leaf on glass . ..12J 
* From comparing the results marked, it appears that the 
effect follows no relation to colour. Softness probably tends 
to increase radiation. 
•f Thickness of film increased beyond a certain limit does 
not increase the radiation. 
J The tenuity is not sufficient to produce any diminution of 
effect, which probably would take place if thinner films could 
be applied. 
4. ) The effect of the surface on radiation is beautifully exem¬ 
plified in the laws which regulate the formation of dew as de¬ 
veloped by Dr. Wells. ( Essay on Dew , 1814. See also Du¬ 
fay. Mem. Paris 1736, p. 352; and Harvey on Dew, Quarterly 
Journ. of Science, No. 33 ; Edinb. Journ. of Science, i. 161.) 
5. ) Dr. Ritchie {Edinb. Phil. Journ . xxiii. 15,) explains his 
theory of the mode in which the radiating power of surfaces is 
increased by making them rough, or furrowing, &c. He con¬ 
tends that it is not owing to the increase of surface, but to the 
quantity of heat reflected by the sides of the furrows. 
He adopts the hypothesis of material caloric, and that its 
molecules are mutually repulsive. 
The effect of surface is an essential distinction between radia¬ 
tion and conduction by air : the latter being shown by Dulong 
and Petit to be absolutely independent of the nature of the 
surface. (. Annals of Phil. xiii. 322.) 
